A lead frame forms the base or skeleton of an IC package, providing mechanical support to semiconductor dies during assembly into a finished package. A lead frame typically includes a die paddle for attaching a semiconductor die, and leads providing the means for external electrical connection to the die. The die can be connected to the leads by wires, e.g. through wire bonding or tape automated bonds. Lead frames are typically constructed from flat sheet metal, e.g. by stamping or etching. The sheet metal is typically exposed to chemical etchants that remove areas not covered by photoresist. After the etching process, the etched frames are singulated (separated) into lead frame strips. Each lead frame strip includes a number of unit lead frames each having the die paddle and lead construction described above.
Semiconductor dies attached to the die paddles after completion of the assembly process of a lead frame strip are usually tested after separation of the unit lead frames from the lead frame strip, e.g. by punching. Alternatively, the unit lead frames remain mechanically connected to the lead frame strip by tie bars during die testing. This is commonly referred to as lead frame strip testing. Separation of the unit lead frames from the lead frame strip occurs after electrical testing. However, the devices must be electrically isolated from one another during lead frame strip testing. Conventional processing involves cutting about half-way through the entire periphery of each unit lead frame to sever the leads, leaving a thin part of molding compound intact in the periphery to hold the units in place during lead frame strip testing. However, such processing increases wearing of the sawing blade which can cause inaccuracy. Also, rigidity of the lead frame strip decreases after the half-cut process, especially for thin packages. In addition a long cycle time is needed to perform the half-cut on the entire lead frame strip, increasing the cost of the individual packages produced from the lead frame strip.